The present invention relates to a non-destructive inspecting method suited for determining the nature or character and size of a reflector of an ultrasonic echo and an apparatus for carrying out the method.
As a method for inspecting a specimen of a metallic material as to the presence of defects such as the one present in the interior of the metal material, fusion failure in a welded portion, slag inclusion and the like, there has been known a method of determining information about these defects on the basis of a frequency spectrum derived through frequency resolution of ultrasonic echoes reflected from the defects. A typical one of such methods is disclosed in U.S. Pat. No. 3,776,026 titled "ULTRASONIC FLAW-DETERMINATION BY SPECTRAL ANALYSIS". According to this method, the size d of a defect is determined on the basis of a frequency spacing .DELTA.f between maxima in the frequency spectrum in accordance with the following expression (1): EQU d=c/.DELTA.f.multidot.sin .theta. (1)
where c represents speed of sound (mm/s) of an ultrasonic wave, .theta. represents an incident angle, .DELTA.f represents the frequency spacing (H.sub.z) between maxima in the frequency spectrum, and d represents the size of a defect.